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Syslog Guide

Sending data to a syslog server where a Splunk forwarder is monitoring the files can improve the data collection to Splunk. A Splunk forwarder automatically load-balances data to all indexers in a distributed environment and can be setup with TLS and other setting to ensure the data transmission is secure and reliable. Utilizing a syslog server will also help prevent gaps in data when Splunk needs to restart for maintenance or unplanned shutdowns. For more information see Splunk answers and Splunk Docs: Forwarder Manual. More information on syslog and Splunk, see the (SYSLOG) Syslog Data Collection section of the Splunk Validated Architectures white paper.

The following will walk through an example of setting up syslog using Rsyslog. Syslog-ng example can be found at the below blog posts:

Data on-boarding using Rsyslog

Rsyslog is a default package on most linux distros. The OPNsense firewall can be setup to send logs via syslog to a configured Rsyslog server for a Splunk Forwarder to monitor. Below is a basic configuration to get started with data on-boarding.

Note

The following does not reflect rsyslog best practices but could be used as a starting point.

Rsyslog Basic Configuration

Tested with Rsyslog version: rsyslogd 8.32.0 on RHEL/CentOS/Ubuntu

The default rsyslog configuration file is located in /etc/rsyslog.conf.

Open the rsyslog configuration file with your favorite text editor. Place the following in the configuration file or uncomment if already present:

Load Modules

Load in the appropriate modules for TCP/UDP

module(load="imudp") # provides UDP syslog reception

File Permissions

The following sets file permissions to root:splunk.

# OMFILE Global Permissions
module(load="builtin:omfile" dirCreateMode="0750" dirOwner="root" dirGroup="splunk" fileCreateMode="0640" fileOwner="root" fileGroup="splunk")

# Legacy Permissions
$umask 0027
$DirCreateMode 0750
$FileCreateMode 0640
$DirGroup splunk
$FileGroup splunk

Event Format Template

The following is a standard example of how to set a template for an event format. This helps to standardize the logs to work better with Splunk.

# Event Template
template(name="t_default" type="list") {
    property(name="timestamp" dateFormat="rfc3339")
    constant(value=" ")
    property(name="fromhost") # can also be set to 'hostname'
    constant(value=" ")
    property(name="syslogtag")
    property(name="msg" spifno1stsp="on")
    property(name="msg" droplastlf="on")
    constant(value="\n")
}

This will create events similar to the following:

2020-02-16T22:47:31-00:00 myserver-003 named[32422]: 136299 10.0.0.5/48300 reply apps.splunk.com is 52.41.47.241

Dynamic File Templates

Create reusable templates for easy change-management

template (name="t_opnsense_filterlog" type="string" string="/var/log/remote/opnsense/%HOSTNAME%/filterlog.log")
template (name="t_opnsense_suricata" type="string" string="/var/log/remote/opnsense/%HOSTNAME%/suricata.log")
template (name="t_opnsense_openvpn" type="string" string="/var/log/remote/opnsense/%HOSTNAME%/openvpn.log")
template (name="t_opnsense_cron" type="string" string="/var/log/remote/opnsense/%HOSTNAME%/cron.log")
template (name="t_opnsense_squid" type="string" string="/var/log/remote/opnsense/%HOSTNAME%/squid.log")
template (name="t_opnsense_lighttpd" type="string" string="/var/log/remote/opnsense/%HOSTNAME%/lighttpd.log")
template (name="t_opnsense_dhcpd" type="string" string="/var/log/remote/opnsense/%HOSTNAME%/dhcpd.log")
template (name="t_opnsense_catchall" type="string" string="/var/log/remote/opnsense/%HOSTNAME%/catchall.log")

Create rulesets

Rulesets can be useful to chain incoming logs to a specific set of rules.

ruleset(name="r_opnsense") {
  if $programname == 'filterlog' then {
    action(type="omfile" dynaFile="t_opnsense_filterlog")
    stop
  }

  if $programname == 'suricata' then {
    action(type="omfile" dynaFile="t_opnsense_suricata")
    stop
  }

  if $programname == 'openvpn' then {
    action(type="omfile" dynaFile="t_opnsense_openvpn")
    stop
  }

  if $programname == 'cron' then {
    action(type="omfile" dynaFile="t_opnsense_cron")
    stop
  }

  if $programname == 'squid' then {
    action(type="omfile" dynaFile="t_opnsense_squid")
    stop
  }

  if $programname == 'lighttpd' then {
    action(type="omfile" dynaFile="t_opnsense_lighttpd")
    stop
  }

  if $programname == 'dhcpd' then {
    action(type="omfile" dynaFile="t_opnsense_dhcpd")
    stop
  }

  *.*   action(type="omfile" dynaFile="t_opnsense_catchall")
}

Input Configuration

Inputs can be specified with a ruleset to tie them to the previously create rules.

input(type="imudp" port="514" ruleset="r_opnsense")

Once the above has been configured, Save & Close the file. Then restart the rsyslog process:

systemctl restart rsyslog

Verify rsyslog is running with: systemctl status rsyslog

Full Example
/etc/rsyslog.conf
# /etc/rsyslog.conf configuration file for rsyslog
#
# For more information install rsyslog-doc and see
# /usr/share/doc/rsyslog-doc/html/configuration/index.html
#
# Default logging rules can be found in /etc/rsyslog.d/50-default.conf


#################
#### MODULES ####
#################

module(load="imuxsock") # provides support for local system logging
#module(load="immark")  # provides --MARK-- message capability

# provides UDP syslog reception
module(load="imudp")
# input(type="imudp" port="514")

# provides TCP syslog reception
#module(load="imtcp")
#input(type="imtcp" port="514")

# provides kernel logging support and enable non-kernel klog messages
module(load="imklog" permitnonkernelfacility="on")

###########################
#### GLOBAL DIRECTIVES ####
###########################
#
# OMFILE Global Permissions
module(load="builtin:omfile" dirCreateMode="0750" dirOwner="root" dirGroup="splunk" fileCreateMode="0640" fileOwner="root" fileGroup="splunk")

# Legacy Permissions
$umask 0027
$DirCreateMode 0750
$FileCreateMode 0640
$DirGroup splunk
$FileGroup splunk

# Event Template
template(name="t_default" type="list") {
    property(name="timestamp" dateFormat="rfc3339")
    constant(value=" ")
    property(name="fromhost") # can also be set to 'hostname'
    constant(value=" ")
    property(name="syslogtag")
    property(name="msg" spifno1stsp="on")
    property(name="msg" droplastlf="on")
    constant(value="\n")
}

#
# Use traditional timestamp format.
# To enable high precision timestamps, comment out the following line.
#
# $ActionFileDefaultTemplate RSYSLOG_TraditionalFileFormat

# Filter duplicated messages
$RepeatedMsgReduction on

# DynaFile Templates
template (name="t_opnsense_filterlog" type="string" string="/var/log/remote/opnsense/%HOSTNAME%/filterlog.log")
template (name="t_opnsense_suricata" type="string" string="/var/log/remote/opnsense/%HOSTNAME%/suricata.log")
template (name="t_opnsense_openvpn" type="string" string="/var/log/remote/opnsense/%HOSTNAME%/openvpn.log")
template (name="t_opnsense_cron" type="string" string="/var/log/remote/opnsense/%HOSTNAME%/cron.log")
template (name="t_opnsense_squid" type="string" string="/var/log/remote/opnsense/%HOSTNAME%/squid.log")
template (name="t_opnsense_lighttpd" type="string" string="/var/log/remote/opnsense/%HOSTNAME%/lighttpd.log")
template (name="t_opnsense_dhcpd" type="string" string="/var/log/remote/opnsense/%HOSTNAME%/dhcpd.log")
template (name="t_opnsense_catchall" type="string" string="/var/log/remote/opnsense/%HOSTNAME%/catchall.log")

ruleset(name="r_opnsense") {
  if $programname == 'filterlog' then {
    action(type="omfile" dynaFile="t_opnsense_filterlog")
    stop
  }

  if $programname == 'suricata' then {
    action(type="omfile" dynaFile="t_opnsense_suricata")
    stop
  }

  if $programname == 'openvpn' then {
    action(type="omfile" dynaFile="t_opnsense_openvpn")
    stop
  }

  if $programname == 'cron' then {
    action(type="omfile" dynaFile="t_opnsense_cron")
    stop
  }

  if $programname == 'squid' then {
    action(type="omfile" dynaFile="t_opnsense_squid")
    stop
  }

  if $programname == 'lighttpd' then {
    action(type="omfile" dynaFile="t_opnsense_lighttpd")
    stop
  }

  if $programname == 'dhcpd' then {
    action(type="omfile" dynaFile="t_opnsense_dhcpd")
    stop
  }

  *.*   action(type="omfile" dynaFile="t_opnsense_catchall")
}

input(type="imudp" port="514" ruleset="r_opnsense")
#
# Where to place spool and state files
#
$WorkDirectory /var/spool/rsyslog
#
# Include all config files in /etc/rsyslog.d/
#
$IncludeConfig /etc/rsyslog.d/*.conf

Troubleshooting

  • Ensure firewall rules are configured to allow the rsyslog listening port (514/udp)
  • Ensure SELinux is not blocking rsyslog from writing to the file. This may occur if you write data outside of /var/log.

Basic Log Rotation Strategy for syslog server

It is necessary to rotate the logs to ensure the disk space does not fill up. Below is a basic example to get started with log rotation.

The following uses the builtin package logrotate. The configuration file can be found at /etc/logrotate.conf

Start by creating a new file in /etc/logrotate.d. For this example, we will use a created file in /etc/logrotate.d/opnsense

Add the following to the file.

/etc/logrotate.d/opnsense
/var/log/remote/opnsense/*/*.log
{
  rotate 7
  daily
  missingok
  create 0640 root splunk
  notifempty
  compress
  createolddir 750 root splunk
  olddir /var/log/remote/old
  dateext
  dateformat -%Y-%m-%d
  dateyesterday
  sharedscripts
  postrotate
          /bin/kill -HUP `cat /var/run/syslogd.pid 2> /dev/null` 2> /dev/null || true
  endscript
}

The above may not work for every situation. Please check the man pages for logroate if experiencing issues. It may also be helpful to look at existing configuration files located in /etc/logrotate.d for reference.

OPNsense Syslog Configuration

The following is necessary to now send syslog data from the OPNsense firewall to the newly configured syslog server.

Administrator access to the OPNsense Web GUI will be required to perform the following steps.

  1. Log into the OPNsense firewall.
  2. Navigate to: System > Settings > Logging/targets.

  3. Click the + (plus sign) to add a new syslog destination.

  4. Ensure the Enabled checkbox is checked.

  5. Transport = UDP(4)
  6. Applications = (Leave Blank) to select everything
  7. Levels = (Leave default setting)
  8. Facilities = (Leave Blank) to select everything
  9. Hostname = FQDN or IP of the syslog server configured in previous steps.
  10. Port = 514

  11. Description = (Optional)

  12. Click Save

  13. Click Apply
Last update: September 26, 2022